Strange Hole-Punch Clouds Explained

Airplanes can punch holes in clouds and make it rain, new research shows. As propeller or jet airplanes pass through the right atmospheric conditions, they make liquid water droplets freeze and immediately drop as snow, leaving a circular fissure behind.

Odd clouds can sometimes elude explanation for decades, and these mysterious gaps in the sky, aptly called hole-punch clouds or channel clouds, have been puzzling sky gazers and scientists alike since the 1940s. A 1968 article in the magazine Weatherwise called them “A Meteorological Whodunit?”

As recently as October 2009, headlines touted a “Mystery UFO Halo Over Moscow.” Earlier studies had suggested a link between hole-punch clouds and airplanes, though the mechanism was unclear.

Previous research also suggests that propeller planes could make snow fall when they flew through supercooled clouds, where water droplets remain liquid despite subfreezing temperatures. But until recently, a direct connection between airplanes, hole-punch clouds and snowfall was missing. Now, a team of atmospheric scientists report observing all three in the June Bulletin of the American Meteorological Society.

Andrew Heymsfield of the National Center for Atmospheric Research and colleagues flew a research plane through the snow produced by a hole-punch cloud west of Denver International Airport in 2007. The plane was loaded with instruments for studying how ice forms in clouds. Radar from the ground picked up a strange echo in their wake, indicating oddly-shaped snowflakes.

“We didn’t know it, but we went right through this precipitation feature that was spotted from the ground,” Heymsfield said.